error-handling-middleware doesn't catch errors outside StandardError

The following controller results in an "empty response" in live mode -- no status code, no nothin.

```
class SomeController < Ramaze::Controller
  map '/err'

  def index
    raise NotImplementedError, "Whatever"
  end
end
```

as demonstrated here:

```
curl logopolis:9292/errs
curl: (52) Empty reply from server
```
